Throughout the United States, especially in the major urban centers, human municipal waste is growing. While the amount of this sludge waste is growing exponentially, the currently approved options for safe disposal of the waste are shrinking. Because pathogenic microorganisms associated with sludge solids can have a prolonged infectious activity, municipal sewage can be a source of microbial pollution in runoff water when sewage sludge is applied to farm lands or landfills without being first sterilized. Further, each of the currently approved options for disposal of this waste is associated with significant drawbacks including expense and environmental concerns.
For example, dumping the human waste into landfills, which was never a desireable option, is becoming even less so as the landfills reach capacity and new locations become increasingly difficult to find. Dumping the waste into the oceans just shifts the environmental problem from one eco-system to another. This method is a form of “looking the other way” as nothing is done to insure that the pathogens in the sludge do not harm the living organisms in the sea.
Burning the waste kills the pathogens and reduces the volume of the waste. The end product of this method is a low analysis “Class A” fertilizer under EPA Rule 503, but it has two major problems. First, the burning process requires large quantities of expensive petroleum to dewater and burn the sludge. As the cost of fossil fuel increases, this method of disposal becomes more and more expensive. Second, the burning process puts carbon and carbon dioxide into the atmosphere, causing other environmental problems.
Composting is another method for disposal of the waste, however, even properly composted sludge has very low plant nutrient value (especially the primary nutrients: nitrogen, phosphorous and potassium). As a result, application of large amounts of compost is necessary and additional nutrients must be furnished to achieve desireable plant growth. Other disadvantages of composting include long processing times (a minimum of 30 to 45 days, weather permitting). The composting process requires turning or stirring and a large land area with an impervious base to prevent vertical leaching. Both horizontal and vertical leaching of nutrients from the compost pile can create additional environmental issues. Further, the smell that is emitted from the pile is highly objectionable to neighboring localities.
In order to apply the sludge direactly to farm land, the sludge must first be stabilized. In one method, high calcium lime and polymeric flocculants are blended into the raw sludge before it is delivered. The raising of the pH by blending in the high calcium lime stabilizes the sludge creating an EPA Rule 503 “Class B” fertilizer. This process reduces the pathogen level in the sludge blend to 90-94% pathogen free. However, the process is expensive and does little to neutralize the ammonia smell odor. The odor is one of the highest sources of complaints and also severly restricts the options for land application due to EPA and State Environmental Agency restrictions based on public health concerns. Land use restrictions include prevention of application of the stabilized sludge to frozen ground. Futher, the farm land once available for lime stabilized sludge operators is increasingly scarce due to urban sprawl.
There are numerous pathogenic microorganisms associated with human sludge which can be a cause of major health concerns. For example, the microorganisms associated with human municipal waste include fecal coliforms, Salmonella species, enteric viruses, and Helminth ova. Some of these microorganisms can pose serious health issues. Members of two bacteria groups, coliforms and fecal streptococci (fecal coliforms), are used as indicators of possible sewage contamination because they are commonly found in human and animal feces. Although they are generally not harmful themselves, they indicate the possible presence of pathogenic (disease-causing) bacteria, viruses, and protozoans that also live in human and animal digestive systems. Therefore, their presence suggests that pathogenic microorganisms might also be present. Since it is difficult, time-consuming, and expensive to test directly for the presence of a large variety of pathogens, water is usually tested for coliforms and fecal streptococci instead. Sources of fecal contamination to surface waters include wastewater treatment plants, on-site septic systems, domestic and wild animal manure, and storm runoff.
Salmonella species are pathogenic bacteria often detected in sewage sludge. Salmonella spp. can survive for long periods in natural waters, and the persistence of specific and epidemic strains is of great concern in public health. Salmonella spp. are ubiquitous enteric bacteria and one of the most common causes of foodborne disease worldwide. These gram-negative rods are the etiologic agents of food-borne salmonellosis and also the agents that cause typhoid and paratyphoid fevers.
Human enteric viruses (i.e., viruses that are transmitted via the fecal-oral tract) consist of more than 100 virus types, with hepatitis A virus and Norwalk virus being the primary human viral pathogens of concern. Human enteric viruses are obligate parasites of man that infect and replicate in the gastrointestinal tract of their hosts. Patients suffering from viral gastroenteritis or viral hepatitis may excrete about 105 to 1011 virus particles per gram of stool, comprising various genera such as adenoviruses, astroviruses, noroviruses, Hepatitis E virus, parvoviruses, enteroviruses (Coxsackie viruses, echoviruses and polioviruses), Hepatitis A virus, and the rotaviruses. Human enteric viruses are causative agents of many non-bacterial gastrointestinal tract infections, respiratory infections, conjunctivitis, hepatitis and other serious infections such as meningitis, encephalitis and paralysis. Most cases of enteric virus infections have been observed to originate from contaminated drinking water sources, recreational waters and foods contaminated by sewage and sewage effluents waters. Wastewater treatment processes such as the activated sludge process, oxidation ponds, activated carbon treatment, filtration, and lime coagulation and chlorination only eliminate between 50% and 90% of viruses present in wastewater, allowing for a significant viral load to be released in effluent discharge. Due to their stability and persistence, enteric viruses subsequently become pollutants in environmental waters resulting in human exposure through pollution of drinking water sources and recreational waters, as well as foods.
Helminth eggs are the infective agents for the types of worm diseases known globally as helminthiases. Although helminths are pluricellular animals their eggs are microscopic (around 20 to 80 μm for those that are important in the sanitary field) and are contained in variable amounts in wastewater, sludge and excreta. Helminth eggs can infect humans through the ingestion of food crops polluted with wastewater sludge or excreta. Due to different health conditions in different countries the type of helminth eggs and their content in wastewater and sludge also varies. Ascaris eggs are the most common and ascariasis is the most common helminthiasis disease worldwide. The content of the other types of helminth eggs in wastewater determines the local patterns of disease.
Accordingly, there is an unmet need for cost effective methods of processing human waste that significantly reduce the pathogen levels of the waste such that restrictions on land application of the processed waste can be lifted and no additional environmental problems are created. The present disclosure provides such improved methods.